Intracranial complications of paranasal sinusitis constitute true surgical and medical emergencies. The charts of all patients (n = 649) admitted for acute or chronic sinusitis to the University of Minnesota Hospital and to the University of Michigan Medical Center during a 13-year period (1975 to 1988) were retrospectively reviewed to determine the incidence of complications. The clinical presentation, bacteriology, involved sinuses, influencing host factors, white blood cell count on presentation, length of hospitalization, and postinterventional complications are presented. Twenty-four patients with intracranial complications from paranasal sinusitis are studied for an incidence of 3.7%. Aggressive medical and semi-emergent surgical intervention are required to prevent excessive morbidity and/or mortality. Intracranial complications included subdural empyema, frontal lobe abscesses, intrahemispheric abscesses, cavernous and superior sagittal sinus thrombosis, and osteomyelitis.